In order to adequately perform transmission control of an automatic transmission for an automobile, the rotational speed of a rotating shaft of the automatic transmission for an automobile, and the torque that is transmitted by that rotating shaft are measured, and the measurement results are used as information for transmission control. As a device for measuring this torque, JPH01254826 (A) discloses a device that converts the elastic torsional deformation amount of a rotating shaft that is transmitting torque to a phase difference between output signals of a pair of sensors, and measures the torque based on that phase difference.
FIG. 58 illustrates a first example of conventional construction of a device for measuring torque that is transmitted by a rotating shaft based on the phase difference between output signals from a pair of sensors. In this torque measurement device, a pair of encoders 2 is fitted and fastened to the outside of a rotating shaft 1 at two locations in the axial direction. The magnetic characteristics of the outer-circumferential surface of the pair of encoders 2, which are detected sections, change in an alternating manner in the circumferential direction and at a uniform pitch. The pitches at which the magnetic characteristics of the outer-circumferential surface of the pair of encoders change in the circumferential direction are the same as each other. A pair of sensors 3 is supported by a housing (not illustrated in the figure) in a state so that detecting sections of the sensors 3 face the outer-circumferential surfaces of the pair encoders 2. The sensors 3 change the output signals in correspondence to the change in the magnetic characteristics of the portions that the detecting sections face.
The output signals from the sensors 3 change periodically as the pair of encoders 2 rotate together with the rotating shaft 1. The frequency and period of the change of the output signal from the sensors 3 are values that correspond to the rotational speed of the rotating shaft 1. Therefore, the rotational speed of the rotating shaft 1 can be found based on the frequency or period of the change in the output signals from the sensors 3. As the rotating shaft 1 undergoes elastic torsional deformation as the rotating shaft 1 transmits torque, the encoders 2 move relatively to each other in the direction of rotation. As a result, the phase-difference ratio (=phase difference/1 period) between the output signals of the pair of sensors 3 changes. Here, the phase-difference ratio between the output signals from the pair of sensors 3 is a value that corresponds to the elastic torsional deformation amount of the rotating shaft 1. Therefore, the torque that is transmitted by the rotating shaft 1 can be found based on the phase-difference ratio between the output signals from the pair of sensors 3.
When this first example of conventional construction is applied to an automatic transmission for an automobile, there is a problem that, due to the high torsional rigidity of the rotating shaft 1, it is difficult to maintain a sufficient elastic torsional deformation amount of the rotating shaft 1, and thus the resolution of the torque measurement becomes low. Moreover, the pair of sensors 3 are located so as to be separated in the axial direction, so there are also problems in that it becomes difficult to arrange two harnesses 4 that run from the pair of sensors 3, and it becomes necessary to provide a pair of supporting and fastening members for supporting the sensors 3 in the housing with a highly precise relative positional relationship.
FIG. 59 illustrates a second example of conventional construction that is disclosed in JPH01254826 (A) in which, together with extending the detected sections of a pair of encoders 2a that are fastened at two locations in the axial direction of the rotating shaft 1 toward the center in the axial direction, the detecting sections of a pair of sensors of one sensor unit 5 that is arranged in the center in the axial direction of the rotating shaft 1 face detected sections of the pair of encoders 2a. However, when this second example of conventional construction is applied to an automatic transmission for an automobile, the torsional rigidity of the rotating shaft 1 is high, so it is not possible to eliminate the problems of not being able to maintain a sufficient elastic torsional deformation amount of the rotating shaft, and the resolution of the torque measurement becoming low.
JPH02017311(U) discloses construction in which a pair of rotating shafts with encoders fastened around the outer-circumferential surfaces are arranged on the same straight line, and the end sections of the pair of rotating shafts are connected to both end sections of a torsion bar that more easily undergoes elastic torsional deformation. In the case of the construction disclosed in JPH02017311 (U), the relative displacement amount in the direction of rotation of the pair of encoders is large, and it is possible to improve the resolution of the torque measurement by that amount. However, when this kind of construction is applied to a counter shaft of an automatic transmission for an automobile, sufficiently increasing the resolution of the torque measurement is difficult. In other words, an input gear and an output gear are fastened to two locations in the axial direction of the counter shaft, and the portion of the counter shaft that undergoes elastic torsional deformation during transmission of torque is only the portion that is between the input gear and the output gear. In this kind of construction, it is necessary to place a torsion bar between the input gear and the output gear, however, the space in the axial direction between the input gear and the output gear is small, so it is not possible to make the dimension in the axial direction of the torsion bar sufficiently long. Therefore, it is not possible to maintain a sufficient amount of elastic torsional deformation of the torsion bar that occurs when transmitting torque, and thus it becomes difficult to sufficiently improve the resolution of the torque measurement.